[Lenka]

If you ask a negative question in English (starting with the verb e.g. Didn't you go to school today?, not You didn't go to school today?), you show your surprise about the thing you ask, right?

But would it also possible that such a negative question wouldn't express the questioner's surprise but would be just an expression of politeness?
For example, imagine the following situation: you meet someone very famous, e.g. Bill Gates. When you meet him, you say: "Good morning, aren't you Bill Gates (by chance - BTW, would it be correct to use "by chance" in auch a context?) ?"

I just wonder if it is possible to ask a negative question in a positive meaning. In fact, you know for sure it's Bill Gates, but to be polite, you ask him the negative question. You expect him to answer "Yes, I am.", not "No, I am not.", actually. Would it be correct?
In German, you can also say (for example) "Sind Sie nicht der berühmte Linguist, der...?" (Are you not the famous linguist, who...?), so I just wonder whether it's all the same in English.